Secure within a desolate home as an unnatural threat terrorizes the world, the tenuous domestic order he has established with his wife and son is put to the ultimate test with the arrival of a desperate young family seeking refuge. Despite the best intentions of both families, paranoia and mistrust boil over as the horrors outside creep ever-closer, awakening something hidden and monstrous within him as he learns that the protection of his family comes at the cost of his soul.